The present invention relates generally to coated substrates and coating materials therefor, and in one particular aspect to fiber-reinforced plastic substrates, such as automotive body panels formed with a sheet molding compound (SMC), that include a sealing primer coating.
As further background, plastics are becoming increasingly important in the construction of automobiles, trucks, off road vehicles, and other products. The materials most commonly used are resins, such as polyamides, polyesters, and urethanes, which are often reinforced with fibers, usually glass fibers.
In many instances, finish coating(s) used on fiber-reinforced plastic substrates such as SMC automotive body panels are cured or otherwise processed at elevated temperatures. Use of such elevated temperatures on the SMC substrates can lead to the evolution of gases from the substrate due to entrapped air and/or other volatile materials which ultimately cause defects in the finished surface such as blisters, craters, “pops” or “vapor boil”.
Attempts to eliminate such defects have included the development of processes in which the substrate to be coated is preheated in order to drive off volatile materials prior to beginning the coating process. As well, SMC and other fiber-reinforced plastic materials have been formulated while attempting to minimize the entrapment of gas or volatile substances such as water in the plastic material, and sealing primer coatings have been developed in an attempt to seal the substrate to minimize or prevent the evolution of gases (including vapors) and thereby protect the applied finish coating.
Despite efforts in the area, needs remain for improved and alternative materials and methods to prevent the formation of defects in finish coatings applied to fiber-reinforced plastic substrates. The present invention is addressed to these needs.